In general, in a system using a server load balancing apparatus (hereinafter, simply called as a load balancing apparatus), connections from user terminals such as personal computers and cellular phones are terminated at the load balancing apparatus, and an appropriate server to which a job for the user terminal is assigned is selected based on load states of the servers and the like to distribute the loads among the servers. At that time, the load balancing apparatus associates the connection with the user terminal side with the connection with the server side, individually, and holds the correspondence data. When receiving request data from user terminal, it transfers the received request data to the server associated with the source user terminal. On the other hand, when receiving response data from the server, it transfers the received response data to the user terminal associated with the source server.
In addition, because it monitors the state of the server, if it detects any trouble in a server at the time of establishing the connection with the user terminal, the server excluded objects of the load balancing. On the other hand, in a case where any trouble occurs in a server in a state in which the connection with the user terminal is already established, the connection with the user terminal side associated with the server is disconnected. Thus, in the user terminal associated with the server in which any trouble occurs, the communication error occurs, and for example, even if a series of jobs were progressed halfway, it is necessary to carry out the jobs again from the beginning.
For example, JP-A-07-240756 discloses a technique in which even if any trouble occurs in a specific communication path, the connection is maintained by using an alternative path. That is, in a case where a connection is established by a path a between a system A and a system B, when the system A detects any trouble in the path a, it transmits a path change request to the system B via a path b. When the system B can use the pass b, it replies a path change confirmation to the system A via the path b. If the transmission path of the path change request is the same as the reception path of the path change confirmation, the system A transmits the pass change confirmation to the system B via the path b. As a result, the connection is maintained by the path b.
However, in the system using the load balancing apparatus, the communication between the user terminal and the server is carried out without recognition of opponent addresses each other. Therefore, it is difficult to simply apply the aforementioned technique to the system using the load balancing apparatus. In addition, in the system using the load balancing apparatus, it is also not appropriate to set an alternative path for each connection between the server and the user terminal in advance.